Ricochet Modem

The reality is that these devices work quite nicely on desktop systems as well as on laptops.

Manufacturer: Metricom, Inc.

E-mail: info@ricochet.net

URL: http://www.metricom.com/

Price: $350 US

Reviewer: Randy Bentson

First a confession, I didn't have to buy a laptop computer to
use the Ricochet modem radio. The reality is that these devices
work quite nicely on desktop systems as well as on laptops.

I read of these modems in the local free computer newspaper,
but since I was quite happy with my 56Kbps frame-relay connection,
I didn't give them much consideration. Then one day my connection
failed and I realized I had no backup for Internet access. After a
quick trip to a local computer store and a few minutes configuring
a PPP connect script, I was back in action. The frame relay was
fixed shortly thereafter, but I still have my Ricochet modem. I use
it when visiting client sites and when testing firewall
configurations, and I used it on the one occasion when the frame
went down again. I've also loaned it to friends suffering from
phone noise and ISP mismanagement.

How Does One Use It?

Plug it into your serial port. It has two connections: one
for external power and one to connect to your computer. The
computer sees it as a Hayes-compatible modem with a few additional
AT (i.e., standard modem) commands.

I mentioned that I had to fiddle with the PPP connection
scripts. As with most computer hardware, Metricom provides software
for operation with the Apple and Microsoft operating systems. Since
Linux comes with support for PPP dial up, there is no need to load
their software. One has only to make some small but crucial changes
to the scripts. The ppp-on-dialer
script needs to send the strings:

ATZ
ATE0X4Q0V1&C1&D2&K3

to the modem to ensure that the configuration is correct. My
ppp-on script needed the line:

route del default

because my system is also on a local LAN and normally gateways
through the frame relay. The phone number, 777**PPP, looks unusual;
it means “connect to the regular Internet service using the PPP
protocol.” The script doesn't need a user name or password because
the modem's serial number is used for authentication. As long as
your account is current, your connection is established with a
dynamically allocated IP address. Listings of these two scripts are
available by anonymous download in the file
ftp.linuxjournal.com/pub/lj/listings/issue45/2493.tgz.

How Does It Work?

First, the Ricochet is not a cell-phone modem. It is based on
an infrastructure which is independent of the various telephone
systems. Metricom has been in the wireless communication business
since 1985—providing remote-access monitoring of meters to public
utilities. The Ricochet division was started two years ago in order
to offer wireless Internet connectivity to the public. They're
currently offering service in the metropolitan areas of Seattle,
San Francisco Bay, West Los Angeles and Washington, D.C. Metricom
plans to extend coverage in the Los Angeles area by the end of this
year and installation is underway in New York City.

If you pay attention, you'll see cell-phone antenna towers or
roof-top clusters appearing everywhere. The Ricochet system is
quite a bit harder to spot. There are three elements: the “modem
radio” attached to your computer, a shoe box sized “microcell
radio” attached to streetlamp poles at quarter mile intervals and
“wired access points” to serve thirty or so microcell radios.
(Seattle has 1800 microcell radios and 50 wired access points.) For
instance, in this map of a Seattle neighborhood the small dots are
the microcell radios, the red stars are wired access points, and
the blue star is the home of Linux Journal.
(The map is a product of a U.S. Census bureau server using the URL
(without breaks) http://tiger.census.gov/cgi-bin/mapbrowser?
lat=47.676&lon=-122.366&wid=0.10&ht=0.050&
on=GRID&murl=http://www.aa.net/~bentson/tms&
iwd=640&iht=720. (See Figure 1.)

Just as the Internet uses a store-and-forward model to get
data from one place to another, Ricochet packets are forwarded from
pole to pole from the modem radio to the wired access point, at
which point they enter the conventional Internet routing. Because
this service is packet based, you don't consume resources when
you're not sending or receiving bits. Therefore, you're welcome to
establish a connection and leave it live for as long as you wish.
This is a dramatic change from telephone-based Internet
services.

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